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B. Volgyi, J. Abdekalimi, S.A. Bloomfield; A Physiological/Morphological Study of the Alpha Ganglion Cells in the Mouse Retina . Invest. Ophthalmol. Vis. Sci. 2003;44(13):5191.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To study the soma-dendritic morphology, tracer coupling pattern, and response properties of alpha ganglion cells in the mouse retina. Methods: Extracellular recordings were obtained from alpha cells visualized by infrared illumination in a mouse retina-scleral preparation. After extracellular recordings, identified cells were intracellularly labeled with Neurobiotin for morphological identification. Results: Identification of alpha cells in the mouse retina was made using criteria established in other mammals, including: (1) largest somata at a given eccentricity, (2) 3-5 thick primary dendrites branching radiantly to form (3) a large, symmetric dendritic field. Similar to descriptions in other mammals, a subset of mouse alpha cells was tracer coupled to 3-6 neighboring alpha cells and to a large number of amacrine cells, wheras others were uncoupled. Interestingly, we found that only off-center alpha cells were tracer coupled, whereas on-center alpha cells were uncoupled. This dichotomy matches that reported by us previously for the rabbit retina. We found that the coupling pattern was unchanged for alpha cells in the connexin36 (Cx36) knockout mouse. Mouse alpha cells showed classic on- or off-center transient responses. Intensity/response functions indicated scotopic responses falling into the intermediate-sensitivity class described recently by our lab (Deans et al., 2002). In addition to the rod-mediated responses, action spectra of alpha cells indicated mixed UV and green cone inputs. As expected from the distribution of cones, alpha cells in ventral retina showed UV-dominant photopic responses, whereas those in dorsal retina showed green cone-dominant responses. In the extreme periphery of the ventral retina we encountered alpha cells with rod and pure UV cone inputs. Likewise, we found alpha cells in the extreme dorsal retina with rod and pure green cone inputs. Conclusions: Alpha cells form a well-defined population of ganglion cells in the mouse as described previously in other mammalian retinas. Although alpha cells show rod-driven activity, they show intermediate scotopic thresholds suggesting that they are innervated through the secondary rod-cone coupling pathway. Alpha cells also show mixed UV/green cone inputs that vary with retinal location. Our finding that alpha cells in wild-type and Cx36 KO mice show similar tracer coupling patterns suggests that Cx36 does not comprise their gap junctions.
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